The present invention relates to a process for producing molten iron from a metalliferous feed material, such as ores, partly reduced ores, and metal-containing waste streams, in a metallurgical vessel containing a molten bath.
The present invention relates particularly to a molten bath-based direct smelting process for producing molten iron from a metalliferous feed material.
The term xe2x80x9cdirect smelting processxe2x80x9d is understood to mean a process that produces a molten metal, in this case iron, from a metalliferous feed material.
The present invention relates more particularly to a molten bath-based direct smelting process that is generally referred to as the HIsmelt process.
In general terms, the HIsmelt process includes thesteps of:
(a) forming a molten bath having a metal layer and a slag layer on the metal layer in a direct melting vessel;
(b) injecting metalliferous feed material and solid carbonaceous material, and optionally fluxes, into the metal layer via a plurality of lances/tuyeres;
(c) smelting metalliferous feed material to metal in the metal layer;
(d) causing molten material to be protected as splashes, droplets, and streams into a space above a nominal quiescent surface of the molten bath to form a transition zone; and
(e) injecting an oxygen-containing gas into the vessel via one or more than one lance/tuyere to post-combust reaction gases released from the molten bath, whereby the ascending and thereafter descending splashes, droplets and streams of molten material in the transition zone facilitate heat transfer to the molten bath, and whereby the transition zone minimises heat loss from the vessel via the aide walls in contact with the transition zone.
A preferred form of the HIsmelt process is characterized by foxing the transition zone by injecting carrier gas, metalliferous feed material, solid carbonaceous material, and optionally fluxes into the bath through lances that extend downwardly and inwardly through side walls of the vessel so that the carrier gas and the solid material penetrate the metal layer and cause molten material to be projected from the bath.
This form of the HIsmelt process is an improvement over earlier forms of the process which form the transition zone by bottom injection of carrier gas and solid carbonaceous material through tuyeres into th bath which causes droplets and splashes and streams of molten material to be projected from the bath.
The applicant has carried out extensive pilot plant work on operating the HIsmelt process with continuous discharge of molten iron and periodic tapping of molten slag from the direct smelting vessel and has made a series of significant findings in relation to the process.
One of the findings, which is the subject of a first aspect of the present invention, is that in situations where there is a continuing supply of oxygen-containing gas and solid carbonaceous material it is possible to hold the process indefinitely, ie stop producing metal, and maintain a pool of molten metal in the vessel, and then continue operating the process and resume metal production.
This is an important finding because there are a number of situations in which it is important to be able to stop production of molten iron for relatively short periods of time. One example of such a situation is when downstream operations can not take molten iron produced by the process. In this situation, whilst the process can continue to operate and produce molten iron, there is a cost penalty associated with not being able to use the molten iron immediately in the downstream processing operations. Another example is where there is an unforseen interruption to the supply of metalliferous feed material to the process and it is not possible to continue operating the process. In such situations, without a hold procedure, the only option is to immediately shut-down the process and empty molten iron and slag from the vessel and then restart the process when the cause of the shutdown has been rectified. A process shutdown/start-up is a major exercise with considerable lost production and cost.
Another of the findings in the pilot plant work, which is the subject of a second aspect of the present invention, is that in situations where there has been an interruption to the supply of solid carbonaceous material but there is an available supply of gaseous or liquid combustible material, such as natural gas, it is possible to hold the process for a considerable period of time, ie stop producing metal, and maintain a pool of molten metal in the vessel, and then continue operating the process and resume metal production.
This is an important finding because, in such a situation, without a hold procedure, the only option is to immediately shut-down the process and empty molten iron and slag from the vessel and then restart the process when the cause of the shutdown has been rectified. A process shutdown/start-up is a major exercise with considerable lost production and cost.
The above findings are applicable particularly to direct smelting processes which discharge molten metal continuously and tap molten slag periodically.
The first aspect of the present invention provides a direct smelting process for producing molten metal from a metalliferous feed material in a vessel that contains a molten bath having a metal layer and a slag layer on the metal layer, which process includes the following standard operating procedure of:
(a) injecting carrier gas, metalliferous feed material, and solid carbonaceous material, and optionally fluxes, into the molten bath via a plurality of solid material injection lances/tuyeres positioned above and extending towards the surface of the metal layer and causing molten material to be projected from the molten bath as splashes, droplets and streams into a space above a nominal quiescent surface of the molten bath to form a transition zone;
(b) smelting metalliferous feed material to metal in the molten bath;
(c) injecting oxygen-containing gas into the vessel via one or more than one lance/tuyere and post-combusting reaction gases released from the molten bath, whereby the ascending and thereafter descending splashes, droplets and streams of molten material in the transition zone facilitate heat transfer to the molten bath;
(d) tapping molten metal and molten slag as required from the vessel;
and which process is characterised by the following hold procedure for situations in which it is necessary to stop production of molten metal for a period of time other than situations in which there has been an interruption to the supply of oxygen-containing gas and/or solid carbonaceous material to the process:
(i) stopping supply of metalliferous feed material into the vessel;
(ii) continuing to inject carrier gas and solid carbonaceous material into the molten bath via the solid material injection lances/tuyeres and generating combustible material in the molten bath and causing molten material and combustible material to be projected into the transition zone; and
(iii) continuing to inject oxygen-containing gas into the vessel via one or more than one lance/tuyere and combusting combustible material projected into the transition zone, whereby the ascending and thereafter descending splashes, droplets and streams of molten material in the transition zone facilitate heat transfer to the molten bath to maintain the temperature of the molten bath above a temperature at which the bath freezes.
Preferably the amount of solid carbonaceous material and oxygen containing gas that is injected into the vessel is reduced during the hold procedure.
Preferably the hold procedure includes periodically adding fluxes to the molten bath.
Preferably the hold procedure includes periodically tapping of molten slag during the hold period.
The second aspect of the present invention provides a process for producing molten metal from a metalliferous feed material in a vessel that contains a molten bath having a metal layer and a slag layer on the metal layer, which process includes the following standard operating procedure of:
(a) injecting carrier gas, metalliferous feed material, and solid carbonaceous material, and optionally fluxes, into the molten bath via a plurality of solid material injection lances/tuyeres positioned above and extending towards the surface of the metal layer and causing molten material to be projected from the molten bath as splashes, droplets and stream into a apace above a nominal quiescent surface of the molten bath to form a transition zone;
(b) smelting metalliferous feed material to metal in the molten bath;
(c) injecting oxygen-containing gas into the vessel via one or more than one lance/tuyere and post-combusting reaction gases released from the molten bath, whereby the ascending and thereafter descending splashes, droplets and streams of molten material in the transition zone facilitate heat transfer to the molten bath;
(d) tapping molten metal and molten slag as required from the vessel;
and which process is characterised by the following hold procedure for situations in which it is necessary to stop production of molten metal for a period of time and there has been an interruption to the supply of solid carbonaceous material to the process:
(i) stopping supply of metalliferous feed material into the vessel; and
(ii) injecting oxygen-containing gas and gaseous or liquid combustible material into the vessel and combusting the combustible material to maintain the temperature.
The term xe2x80x9ccombustible materialxe2x80x9d in regard to the first aspect of the invention is understood to include, by way of example, carbon monoxide, solid char, and hydrogen and other volatiles that may be generated from a solid carbonaceous material.
The term xe2x80x9cquiescent surfacexe2x80x9d in the context of the molten bath is understood to mean the surface of the molten bath under process conditions in which there is no gas/solids injection and therefore no bath agitation.
Typically, the hold period of time is up to 5 hours.
Preferably, step (d) of the process includes continuously tapping molten metal from the vessel.
Where the process includes continuously tapping molten metal via a forehearth, preferably the hold procedure includes varying the pressure in the vessel and thereby varying the level of molten metal in the vessel and forcing molten metal from the vessel into the forehearth and from the forehearth into the vessel. Varying the pressure causes circulation of molten metal between the vessel and the forehearth and assists in maintaining a relatively uniform temperature of the molten metal in the vessel and the forehearth.
Preferably the solid carbonaceous material is coal.
Preferably the gaseous combustible material includes natural gas.
Preferably the oxygen-containing gas is air or oxygen-enriched air.
More preferably the oxygen-enriched air contains less than 50% by volume oxygen.
Preferably the process operates at high post-combustion levels.
Preferably the post-combustion levels are greater than 60%.
Preferably, the metalliferous feed material is an iron-containing feed material. The preferred feed material is iron ore.
The iron ore may be pre-heated.
The iron ore may be partially reduced.
Preferably metalliferous feed material is smelted to metal predominantly in the metal layer.